Information on the black rhinoceros population of Nairobi National Park has been obtained from two-month surveys in 1967 and 1968 backed by data collected at random over the past few years. It proved impossible to identify some of the rhinoceroses whose presence was indicated by spoor and unidentified sightings, and an estimate of the total number present at the end of 1968 must vary between 27 and 33 animals. Twenty-two rhinoceroses have been brought into the Park by the Game Department Capture Unit since November 1966. The fate of these animals has been: two dead, two not seen and 18 identified in the Park 3–33 months after release. The newcomers have produced only one serious conflict with a resident rhinoceros and two collisions with motor vehicles. Despite the small size of the Park, the inadequacy of its boundaries and the legendary intolerance of the species, it would appear that the translocation operations have been a success.